Children who live in areas with high levels of noise, like those next to busy roads, are more stressed

Living in an area with constant background noise, such as traffic, raises children's blood pressure and stress levels.

Even though levels of noise from cars or trains may not be high enough to damage hearing, US and Austrian scientists report in New Scientist that constant, low-level sound can affect children.

In a study commissioned by the Austrian Ministry of Health, it was found the noisier the neighbourhood, the higher the children's blood pressure, heart rate and level of stress hormones.

The study suggests that a child's "motivation" could also suffer from prolonged exposure to noise.

Children living in noisier areas of residential communities are subject to stress

Gary Evans,Cornell University, New York

UK experts said it was known the health of people living under flight paths suffered through prolonged exposure to noise.

Study author Gary Evans from Cornell University, Ithaca, New York , said they had not been looking at loud levels of noise.

And he said that the low levels examined were typical levels found throughout neighbourhoods in Europe.

"It suggests that children living in noisier areas of residential communities are subject to stress."

He added: "We don't know much about the non-auditory health effects of exposure to everyday noise at lower intensity."

Previous studies have looked at the effect on hearing of loud noise from airports and railway lines.

But they said the long term effects of exposure to noise now needed to be studied.

Health checks

In the study, 115 children aged nine and 10 from alpine villages in Inn Valley, Tyrol, Austria were tested for blood pressure, heart rate, cortisol and adrenalin levels, while they were at rest.

The children were grouped into those who lived in areas with noise levels of less than 50 decibels and those who lived in a place which had noise levels higher than 60 decibels.

It was found background noise had a "significant effect" on stress levels.

The study also gave the children questionnaires and motivation tasks, and found this kind of stress can affect motivation.

They said it seemed to lead to "learned helplessness syndrome".

The syndrome has been linked to poverty and some kinds of depression.

Gary Evans said: "It's a pretty pervasive phenomenon. Girls in particular seem to be a little bit more vulnerable to learned helplessness."

Researcher Peter Lercher, from the Institute of Social Medicine at the University of Innsbruck in Sonnenburgstrasse, said: "Anything that increases blood pressure over time is something to worry about."

John Stewart, chairman of the UK Noise Association in London said the study echoed anecdotal reports from people living under flight paths who said even when levels were within recommended safety limits, noise could still be bad for your health.

"This is precisely the kind of issue that governments have failed to acknowledge for years. What they really refuse to look at is lower levels of noise that is fairly constant."